In an existing printer, a printing system carries a plurality of pens as illustrated in FIG. 1, each pen 10, 11 including a plurality of nozzles 100, 110, the nozzles forming two columns along the length of the pen, the length of the pen corresponding to the printing medium direction 1. The pens are located beside each other along the scan axis 2. Each pen is in theory perfectly aligned with the other pen, so that each nozzle 100 is associated and perfectly aligned to the corresponding nozzle 110 situated at the same level along the scan axis 2. In practice, as illustrated in FIG. 2, it may occur that a pen 12 results misaligned in the printing medium direction 1 with another pen 10. As a result, the nozzle 120 should not be associated with the theoretically corresponding nozzle 100, but with the following nozzle 101. It should be noted that in this particular case, there are four nozzles, 2 for each pen, which may be associated as being aligned along the printing medium direction. This is a reason to detect and estimate the alignment in the printing medium direction between a first and a second pen. In the existing printer, such an estimate is provided by scanning a dedicated interference pattern or by scanning a series of biased lines printed by each of the pens. Such methods of estimate are known in the art.
Separately, in an existing printer, the alignment of a nozzle in the scan axis is also estimated, this estimate being made by scanning a different pattern, this pattern being made of blocks. This estimate may be taken into account to be corrected in order to improve the quality of printing. If for example a nozzle is displaced towards one side of the scan axis, this displacement may be compensated by triggering the nozzle with an advance or with a delay. Such methods of compensation are known in the art.